Enhanced macroparticle filter and cathode arc source

ABSTRACT

A cathode arc source for depositing a coating on a substrate has an anode and a cathode station for a target, a first filter means comprising a filter duct having at least one bend, and first magnetic means for steering plasma through the filter duct for removal of macroparticles from the plasma. The apparatus comprises a second filter ( 10 ) for further removal of macroparticles from the plasma, made up of a baffle ( 11 ), an aperture ( 12 ) through which plasma can pass and second magnetic means ( 13 ) for steering plasma through the aperture. The aperture size may be less than 33% of the duct sectional area at that point. The source can also include an ion beam generator. Also described is a method of depositing coatings of ions using the second filter and closing the aperture in the filter when required.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of allowed U.S.application Ser. No. 09/530,009, which is a U.S. National Phase ofInternational Application No. PCT/IB98/01764, filed Oct. 26, 1998, whichis incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0002] The present invention relates to deposition of coatings using acathode arc source, to filtering of macroparticles from plasma in acathode arc source, in particular using a magnetically enhancedmacroparticle filter, and to substrate preparation prior to depositionand to control of deposition.

[0003] Cathode arc deposition of tetrahedral amorphous carbon, metallic,dielectric and other such coatings are known in the art and offer thepotential for deposition of thin films of high quality. Applications inscratch resistant optical coatings and hard disc media coatings are buttwo of a wide range of proposed uses.

[0004] Hitherto, deposition of films by the cathode arc process has beenlimited to laboratory use, in general because of difficulties in the artin reliably depositing films that are free of or have acceptably lowcontamination by macroparticles—large, neutral particles.

[0005] Provision of improved means for filtering macroparticles from thearc plasma have recently been described in WO-A-96/26531 and also inInternational patent application no. PCT/GB97/01992. Nevertheless,further improvements in filtering of macroparticles is desirable andwill become more so as further applications for the deposited filmsarise.

[0006] The present inventors have identified problems with deposition ofthin films using arc plasma, namely that the initial period ofdeposition can give a poor quality coating; it would therefore bedesirable to avoid deposition using the plasma first emitted afterstriking an arc at a target. Likewise, the final period of depositionwhile the plasma density is falling, just before breakdown of the arc,can also give poor quality coatings, and it would be desirable to avoiddeposition at this time. Known filtered cathode arc sources do nothowever have such a facility.

[0007] It is vital in some applications to be able to provide anaccurate thickness of coating and to stop deposition when the desiredthickness has been achieved. However, there is a period of seconds aftershutting down the arc during which there is a small residual amount ofdeposition—this can lead to a slightly greater coating thickness than iswanted. Existing apparatus does not enable deposition to be stoppedsuddenly.

[0008] Tetrahedral amorphous carbon coatings laid down using filteredcathode arc apparatus can be liable to tear or peel away from asubstrate and, in an attempt to avoid or reduce this, pretreatment ofthe substrate to clean the surface that will receive the coating isoptional, but can hitherto only be carried out either in apparatusseparate from the deposition apparatus or in deposition apparatusincorporating an ion beam source in addition to a cathode arc source.The former inconveniently introduces an extra step into production ofcoatings, unattractive from a commercial point of view, as well asrequiring two separate machines. Deposition apparatus with their own ionbeam source are expensive as the ion beam source is a separateattachment to the chamber.

[0009] The present invention seeks to provide for further filtering ofarc plasma and to overcome or at least ameliorate problems encounteredwith prior art cathode arc sources. It is therefore an object of theinvention to provide method and apparatus for filtering macroparticlesfrom plasma in a cathode arc source. A further object is to facilitatedeposition of coatings on substrates that have been pretreated topromote adhesion of the coating thereto.

SUMMARY OF THE INVENTION

[0010] Accordingly, a first aspect of the invention provides a cathodearc source for depositing a coating on a substrate, said sourcecomprising:

[0011] an anode and a cathode station for a target,

[0012] a first filter means comprising a filter duct having at least onebend, and

[0013] first magnetic means for steering plasma through the filter ductfor removal of macroparticles from the plasma;

[0014] wherein the apparatus comprises a second filter for furtherremoval of macroparticles from the plasma, the second filter comprisinga baffle, an aperture through which plasma can pass and second magneticmeans for steering plasma through the aperture.

[0015] An advantage of the apparatus of the invention is that furtherfiltering of macroparticles is provided which can result in furtherimprovements in the quality of films, such as tetrahedral amorphouscarbon films, deposited from the cathode arc source. The aperture ispreferably closeable. The first aspect of the invention also providesthe second filter in isolation from the rest of the apparatus.

[0016] In an embodiment of the invention, the second filter is locatedbetween the duct of the first filter and the substrate. In use, plasmacontaining positive ions and being contaminated by macroparticles issteered around the bend of the first filter and a proportion ofmacroparticles hit the side of the filter duct and are removed from theplasma. At the end of the duct closest to the substrate, that is to sayafter the plasma has passed through the bend, there is a relatively highdensity of the remaining macroparticles towards the outside of the duct.The plasma is however more dense in terms of positive ions towards thecentre of the duct. The second filter of the invention thus is effectivebecause its baffle is located towards the outside of the duct and thusmacroparticles towards the outside of the duct hit the baffle and areprevented from travelling further towards the substrate.

[0017] A preferred embodiment of the source of the invention thuscomprises a first filter duct attached to a chamber in which plasma isdeposited on a substrate, wherein the second filter means is located ator near the exit of the filter duct and exerts its filtering effectbefore the plasma reaches the chamber.

[0018] It is further preferred that the second filter means is in theapproximate form of a disc having a substantially circular aperture. Asplasma in the duct is denser towards the duct centre and can be steeredthrough a circular aperture this is a convenient configuration of theaperture to obtain high transmission of plasma through the second filterwhilst filtering macroparticles from the plasma. The aperture shape mayadditionally be at least partially dictated by the cross-section of thefilter duct. If this were not circular but oval-shaped, then anoval-shaped aperture or an aperture varying from circular might beappropriate.

[0019] A typical filter of the invention extends across the width of thefilter duct. Macroparticles that hit the baffle of the disc fall backonto the side of the duct away from the substrate; after a period of useit will be preferred to clean the duct and/or the disc in this area,though a major part of the filtering is achieved by the first bend ofthe duct and consequently cleaning of the filter disc will not often benecessary.

[0020] In an embodiment of the invention shown in an example below, thefilter disc is a substantially planar and circular disc of steel foilwith a central aperture. In another embodiment of the invention shown inanother example below the filter disc is not planar but comprises abaffle angle to deflect macroparticles away from the plasma. Anadvantage of this embodiment is that the purpose of the baffle it toreduce the number of macroparticles that reach the substrate. Somemacroparticles when stopped by the baffle may be deflected into theplasma beam and thereafter carried towards the substrate by the plasmamomentum. A baffle that is inclined to the plasma so as to deflectmacroparticles away from the plasma and towards the side of the duct isthus a preferred component of the filter.

[0021] Generally, the disc should be thin and should not interfere withoperation of the filter duct and should not interfere with the magneticfield that steers plasma through the filter duct. Typically, the disc isless than 2 mm thick, and is preferably less than 1 mm thick.

[0022] The aperture in the filter is for passage of plasma therethroughand may be less than 33% of the internal sectional area of the filterduct at that point, preferably less than 25% of the duct internalsectional area, i.e. for a circular aperture in a circular duct, lessthan 50% of the internal width of the filter duct. Good results havebeen achieved using a filter having an aperture size of less than 16%duct sectional area, i.e. about 40% the width of the duct. Morepreferably, the aperture size is less than 9% duct sectional area andmost preferably still, an aperture size of less than 5% duct sectionalarea is used. The aperture will be designed according to its particularapplication and different sizes may be appropriate according to theposition of the filter, the size of the filter duct and the type ofmaterial that is being laid down in a coating. If the radius of thefirst bend of the filter duct is sharp the density of macroparticlestowards the outside of the duct may be higher, as macroparticles are notbent around the bend by the magnetic steering field, in which case asmaller baffle and a larger aperture may be suitable.

[0023] Table 1 below shows the relationship between filter aperture sizeand percentage internal sectional area of the filter duct for a 150 mm(6 inch) or a 200 mm (8 inch) double bend filter. % Duct Sectional Area% Duct Sectional Area Aperture Size 150 mm (6 inch) duct 200 mm (8 inch)duct 35 mm  5.4%  3% 45 mm   9%  5% 60 mm   16%  9% 80 mm 28.4% 16%

[0024] Plasma density generally increases towards the centre of the ductand thus only a small proportion of plasma is blocked by the action ofthe second filter. Even so, it is preferred that the apparatus comprisesone or a plurality of permanent magnets for providing a local magneticfield around the second filter to steer plasma away from the baffle andthrough the aperture. This is of advantage in that the proportion ofplasma passing through the filter is increased whilst the steering fielddoes not directly increase the passage of macroparticles through theaperture of the filter. By use of a magnetic steering field in additionto and separate from that used to guide plasma around the bend of thefilter duct a magnetic field locally enhanced in the region of thesecond filter is provided to pinch plasma through the aperture, whichmay as a result be made smaller whilst allowing substantially all plasmato pass. A reduction in size of the aperture further increases thefiltering of macroparticles from the beam.

[0025] Permanent magnetics offer the advantage that no electricalconnection need be made from outside the duct into a coil or coilslocated within the duct. Alternatively, the apparatus comprises anelectromagnetic coil for providing a local field around the secondfilter, adapted for connection to an external power supply.

[0026] In use, the magnetic field around the second filter may have astrength in the range of 100 to 200 Gauss, though a stronger fieldstrength may be appropriate if increased filtering is required and maythen facilitate a further reduction of the filter aperture.

[0027] It is optional for the second filter to be composed of a baffleplate that is located only on one side of the duct. The filter of thisembodiment is thus not a disc having a hole or aperture but a plate;plasma is steered around the plate by a locally enhanced magnetic fieldand macroparticles hitting the plate are thereby prevented from reachingthe substrate.

[0028] Further embodiments of the invention relate to rapid control ofdeposition and to substrate preparation. Accordingly, a particularapparatus of the invention additionally comprises a shutter associatedwith the second filter for opening and closing of the aperture.Operation of the shutter between a closed and an open positionrespectively stops and starts deposition during use of the cathode arcsource. Deposition can be stopped and started at precise times, andrapidly. To avoid deposition during the period immediately after arcstriking the shutter can be closed initially and then opened afterplasma quality has reached a predetermined level or after apredetermined time. This feature of the invention can thus offerimproved control over the deposition process.

[0029] The shutter is optionally controlled manually by handle meansextending from the shutter outside the filter duct. The shutter may alsobe controlled by an actuator in operative combination with controllingcircuitry of the cathode source and adapted to close the shutter inresponse to certain predetermined states of the arc. One such state maybe a drop in plasma quality. Another may be a drop in plasma density.

[0030] A shutter described specifically below comprises twosubstantially semi-circular halves adapted for movement across theaperture between retracted positions away from the aperture and closedpositions in which they meet in front of and obscure the aperture. Theparticular shutter described is water-cooled.

[0031] A yet further particular embodiment of the invention lies in acathode arc source for depositing a coating on a substrate, said sourcecomprising:

[0032] an anode and a cathode station for a target,

[0033] a first filter means comprising a filter duct having at least onebend, and

[0034] first magnetic means for steering plasma through the filter ductfor removal of macroparticles from the plasma;

[0035] wherein the apparatus comprises a second filter for furtherremoval of macroparticles from the plasma, comprising a baffle, anaperture through which plasma can pass and second magnetic means forsteering plasma through the aperture, further comprising

[0036] means in a deposition chamber for generating an ion beam anddirecting said beam at the substrate.

[0037] A still further particular embodiment of the invention lies in acathode arc source for depositing a coating on a substrate, said sourcecomprising

[0038] an anode and a cathode station for a target,

[0039] a first filter means comprising a filter duct having at least onebend, and

[0040] first magnetic means for steering plasma through the filter ductfor removal of macroparticles from the plasma;

[0041] wherein the apparatus comprises a second filter for furtherremoval of macroparticles from the plasma, comprising a baffle, anaperture through which plasma can pass and second magnetic means forsteering plasma through the aperture,

[0042] wherein the second filter comprises means for generating an ionbeam and directing said beam at the substrate.

[0043] Cleaning of the substrate prior to deposition or other surfacetreatment of the substrate prior to deposition can thus be easily andconveniently carried out using these embodiments of the invention. Anion beam in the chamber or associated with the second filter can beoperated before beginning to deposit a coating. Another possibility isto use the ion beam between laying down different layers in amulti-layer coating.

[0044] The ion beam generating means is suitably of the “end-hall” ionbeam type, and may comprise one or a plurality of electric filaments. Aspecific second filter of the invention comprises a plurality offilaments for generating electrons for an ion beam source, locatedsubstantially evenly spaced around the aperture of the filter. A sourceof gas, such as Argon, is located at or near the second filter.

[0045] The invention also provides a method of filtering macroparticlesfrom a beam of plasma emitted from a cathode arc source, the methodcomprising:

[0046] steering the beam through a first filter comprising a filter ducthaving at least one bend; and

[0047] steering the beam thereafter through a second filter comprising abaffle and an aperture through which plasma can pass.

[0048] A preferred method is one comprising steering the beam throughthe second filter by steering the beam using a magnetic field locallyincreased in strength around the second filter. Thus plasma ispreferentially steered around and to avoid the baffle whereas aproportion of macroparticles, not being so steered, hit the baffle andare deflected away from and prevented from reaching the substrate.

[0049] A further aspect of the invention provides a method of depositinga coating on a substrate using deposition apparatus comprising a cathodearc source, the method comprising:

[0050] positioning the substrate in a deposition chamber of theapparatus,

[0051] directing at the substrate an ion beam, and

[0052] depositing on the substrate a coating of positive ions emitted ina plasma from the cathode arc source.

[0053] The ion beam may be generated from ion beam generating meanslocated inside the deposition chamber.

[0054] In another embodiment of the invention the apparatus comprises afilter duct between the deposition chamber and the cathode arc source,and wherein the ion beam is generated from an ion beam generating meanslocated in the filter duct, at or near the exit of the duct into thechamber. A shutter is conveniently located in the filter duct and themethod may then comprise the steps of closing the shutter, directing anion beam at the substrate, opening the shutter and depositing a coatingof positive ions on the substrate.

[0055] The invention still further provides a method of depositing acoating on a substrate using deposition apparatus comprising a cathodearc source, the method comprising:

[0056] depositing on the substrate a coating of positive ions emitted ina plasma from the cathode arc source,

[0057] monitoring the thickness of the coating, and

[0058] when the thickness has reached a predetermined level, moving ashutter across the plasma so as to prevent further deposition of plasmaon the substrate.

[0059] The invention still further provides a method of depositing acoating on a substrate using deposition apparatus comprising a cathodearc source having an anode and a cathode target for emission of a plasmacontaining positive ions and a filter duct for filtering ofmacroparticles from the plasma, the method comprising

[0060] moving a shutter across the filter duct so as to preventdeposition of plasma on the substrate,

[0061] striking an arc between the anode and the target,

[0062] determining when plasma quality has reached a predeterminedlevel, or waiting a predetermined period of time, and

[0063] opening the shutter so as to allow deposition of plasma on thesubstrate.

[0064] A still further aspect of the invention provides apparatus forgenerating plasma for deposition upon a substrate, said apparatuscomprising a first cathode arc source, a second cathode arc source and amain plasma duct, wherein plasma output from the first cathode arcsource is guided into the main duct via a first side duct connected tothe main duct, plasma output from the second cathode arc source isguided into the main duct via second side duct connected to the mainduct, and wherein a single plasma is output from the main duct of theapparatus.

[0065] During operation of the apparatus, if plasma is being generatedfrom both the first and second cathode arc sources, the plasma outputsare combined in the main duct to form a single plasma output fordeposition onto a substrate. Alternatively, the first and second cathodearc sources can be operated independently of each other, so that one arcsource is in use at a time, e.g. whilst the other is being serviced.

[0066] The apparatus offers the advantage that increased rate ofdeposition can be achieved using both sources simultaneously with theiroutputs combined. The apparatus also offers the advantage thatmulti-layer coatings can be provided by operating a first source with atarget of one material and the second source with a target of adifferent material. One example is to operate a first source with asilicon target and a second source with a graphite target.

[0067] The apparatus comprises magnetic field generating means, such asan electromagnet or a permanent magnet, to guide plasma output from therespective sources via the side ducts into the main duct. The apparatusfurther preferably comprises magnetic field generating means locatedbelow the target in each source so as to provide a point of zero normalfield strength above the target and strong lateral field at the surfaceof the target as the resultant of the field below the target and theguiding field, which are of opposite direction.

[0068] In a preferred embodiment of the invention, the main duct issubstantially linear with one end attached to or opening into orotherwise in communication with a deposition chamber, and the side ductsare attached to the main duct substantially opposite each other. A viewport or a monitor of deposited film thickness can be convenientlylocated at the end of the main duct opposite to the end connected to adeposition chamber. This is an advantageous arrangement in that there isa line-of-sight directly from that end of the main duct to thesubstrate. This is illustrated for example in a specific embodiment ofthe invention discussed below and shown in FIG. 5.

[0069] It is further preferred that, for deposition of coatings thatcomprise oxide, the apparatus is adapted for introduction of argon gasinto the main duct, via inlet port in the main duct and/or in the sideducts, whilst oxygen is introduced into the deposition chamber. A portis optionally provided in the main duct so that argon gas can beintroduced at an end of the main duct proximal to the deposition chamberand pumped out distal to the deposition chamber so as to maintain apartial pressure of argon in the main duct sufficient to reduce entry ofoxygen into the main duct and from there into the side ducts where theanodes of the sources are, whereby oxide contamination of targetmaterial is reduced. This argon partial pressure may optionally be atleast around 10⁻⁴ torr. With an oxygen partial pressure in thedeposition chamber of about 10⁻²-10⁻³ torr oxygen is largely preventedfrom entering the main duct by such a partial pressure of Argon, isconsequently largely prevented from entering side ducts and thereforethere is minimum contamination of the cathode arc source by build up ofoxide on the anode surface.

[0070] It is also preferred that the cathode arc sources are shieldedfrom external magnetic fields, such as the guiding fields, by the use ofa shroud of material having high magnetic permeability. Iron and theso-called “μ-metals” are suitable. It is an option to operate theapparatus without using the “reversing” field located at or below thetarget so long as the cathode arc sources are shielded from excessiveinfluence by the guiding field required to guide the plasma outputtowards the substrate.

[0071] In another embodiment of this aspect of the invention, the mainplasma duct comprises at least a single bend for filtering ofmacroparticles from the plasma. The bend angle is optionally 30-90°.Apparatus of this aspect of the invention can be combined with adeposition chamber so that a substrate can be coated simultaneously onboth its front and rear surfaces. Thus, a deposition apparatus maycomprise a deposition chamber to two sides of which are attachedapparatus according to this aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

[0072] The invention is now illustrated with reference to drawings inwhich:

[0073] FIGS. 1(a) and (b) show a schematic front view and a schematiccross-section of a filter disk according to the invention;

[0074] FIGS. 2(a), (b) and (c) show schematic views of a filter disk ofthe invention in first and second positions and a schematiccross-section of the filter in a first position;

[0075] FIGS. 3(a), (b) and (c) show schematic views of a filter disk ofthe invention in first and second positions and a schematiccross-section of the filter in a first position;

[0076] FIGS. 4(a), (b) and (c) show images of films obtained,respectively, by prior art techniques, using a double bend as describedin WO-A-96/26531 and, finally, using a magnetically enhanced filteraccording to the present; and

[0077]FIG. 5 shows a schematic cross-section of a deposition apparatusof the present invention comprising two cathode arc sources.

[0078]FIG. 6 shows the relationship between aperture size in the secondfilter (% sectional area of the filter duct) and stress of a ta-C film.

[0079]FIG. 7 shows the relationship between aperture size in the secondfilter (% sectional area of the filter duct) and macroparticle count atthe substrate.

[0080]FIG. 8 shows the relationship between aperture size in the secondfilter (% sectional area of the filter duct) and deposition rate.

DETAILED DESCRIPTION OF THE INVENTION

[0081] Referring to FIGS. 1(a) and (b), a filter disk is shown generallyas 10 and is made of stainless steel foil less than 1 mm thick. Thefilter comprises a baffle 11 and an aperture 12. A permanent ring-magnet13 (or an electro-magnet 13) is located around the periphery of the diskand in use provides a locally enhanced magnetic field so as to steerplasma through the aperture 12, allowing neutrally chargedmacroparticles to hit the baffle 11 and travel no further towards thesubstrate. FIG. 1(b) shows a schematic cross section of the diskillustrated in FIG. 1(a). The aperture 12 is normally in the size range10 to 50 mm for use in a filter duct having an internal diameter ofabout 100 mm.

[0082] Referring to FIGS. 2(a), (b) and (c) and FIGS. 3(a), (b) and (c),a filter disk of the invention is shown generally as 20 and comprises abaffle 21 and aperture 22. A circular permanent magnet 23 (orelectromagnet 23) is located at the periphery of the filter disk andprovides a locally enhanced magnetic field to steer plasma through theaperture. As discussed above, the locally enhanced magnetic field canalso be provided by an electromagnet.

[0083] The embodiments of the invention shown in these two figuresinclude a shutter composed of shutter portions 26 which when in a closedposition, shown in FIGS. 2(a) and 3(a), closes the aperture 22, and whenmoved to an open position, shown in FIGS. 2(c) and 3(c) allows a plasmabeam emitted from the cathode arc source to pass through the apertureand reach the substrate. The shutter portions 26 are made also of steeland are cooled by flow of water through cooling pipes 27. In thearrangements shown, the cooling pipes are attached to the shutterportions and mounted for pivotal movement on pivots 28. A handle foropening and closing of the shutter by an operator is attached, but notshown in these figures. The shutter with cooling pipes attached islocated on duct side 24 of the apparatus and not on chamber side 25. Ifthe shutter is made of graphite then the cooling pipes can be omitted.

[0084] An ion beam attachment, for generation of an ion beam forcleaning the substrate prior to deposition or for carrying out other ionbeam treatments of the substrate surface is optionally attached to orassociated with the filter disk, usually located on the chamber side 25of the filter disk assembly.

[0085] When the ion beam attachment is working, a filament or filaments17 attached to the chamber side 25 provide electrons and permanent ormagnet 23 provide the magnet field necessary for the electrons to startand sustain the plasma discharge on the chamber side. The disk 20 ispositively biased (typically up to +150V) to act as the anode and theshutter is closed, acting as the reflector (with a floating voltage).Thus, an ion beam is generated and directed towards the chamber. Thedisc design shown in FIG. 3(b) is preferred in this respect as itproduces a slightly more focused ion beam. The ion beam source is thusof the “end hall” type.

[0086] Use of the magnetically enhanced filter of the invention has beentested by the inventors and a film has been deposited using themagnetically enhanced filter and compared with films obtained via priorart techniques.

[0087] The results are shown in FIGS. 4(a), (b) and (c).

[0088]FIG. 4(a) shows a film deposited using prior art techniques. Thedark blemishes are large, neutrally-charged macroparticles contaminatingthe film. They are seen to be numerous in this prior art film.

[0089] FIG.4(b) shows the film deposited using a double bend filter ductas described in WO-A-96/26531, with reduced contamination bymacroparticles, though nevertheless with a number of macroparticlesvisible.

[0090] Lastly, FIG. 4(c) shows a film deposited using depositionapparatus having a double bend filter duct and a magnetically enhancedfilter according to the invention. Fewer macroparticles are seen in thisdeposited film and in the area of film shown there are nomacroparticles.

[0091] Referring to FIG. 5, deposition apparatus shown generally as 30comprises two cathode arc sources 31 and 32. Each cathode arc sourcecomprises a target 33, in electrical contact with a target plate 34 anda cathode body 35. The combination of a target plate 34 and a cathodebody 35 are also referred to as a cathode station—ie for location of acathode target thereon and electrical connection to the arc powersupply.

[0092] In use, cooling of the target is achieved via flow of coolingwater into the inlet 36 and exiting via the outlet 37.

[0093] A so-called “reversing field” is provided by permanent magnet 38mounted around and below the lower part of the target. The permanent 38may optionally be replaced by an electromagnet. Magnets or coils for aguiding field to guide plasma from the target towards a substrate arenot shown but are located around the side ducts 39.

[0094] Around the target 33 is provided a shield composed of a shieldbody 40, a ceramic circle 41 and shield cap 42. An anode liner is fittedtightly inside and in electrical contact with anode wall 44. Cooling isprovided by flow of water through the cooling water housing 45 andobservation of the arc is through view port 46. A linear striker 47 isprovided for arc striking.

[0095] The deposition apparatus comprises a chamber, not shown, which isat position 48 attached to main duct 49 by flange 50. Guiding of plasmatowards a substrate in the chamber is achieved by conventional magneticfields generated by guiding field coil 51 and enhancing field coil 52.The guiding field within the main duct is typically of strength between400 and 1000 Gauss, while the guiding field within the side ducts istypically of strength between 200 and 600 Gauss, with the magnetsproviding the fields being conveniently arranged so as to provide acontinuous guiding field through the side duct, into the main duct andonto a substrate in a deposition chamber.

[0096] The fields can alternatively be generated by permanent magnets.The main duct 49 and its coils or other magnets and the side ducts andits guiding coil or magnets are optionally shrouded by a shroud, notshown, of material of high magnetic permeability—iron or μ-metals aresuitable. The effect of the shroud is to reduce the influence of theguiding fields on the field at and around the target.

[0097] In the embodiment illustrated, the diameter of the side ducts isabout 15 cm (6 inches) and that of the main duct is about 20 cm (8inches). Other diameters can also be adopted though the diameters of theside ducts will conveniently be less than that of the main duct.

[0098] At position 53 may be mounted one or more of a viewport, an ionbeam source, a monitor of the thickness of the film deposited on thesubstrate and a pumping port. Flange 50 may also comprise or be part ofa valve for isolation of the main and side ducts from the chamber 48 forthe purpose of servicing the sources. A pumping port is then used toevacuate the main and side ducts before reopening this valve. Theapparatus can also include a magnetically enhanced filter according tothe invention, located so as to filter macroparticles in the main duct,or in the side ducts, or both.

[0099] Referring to FIG. 6, the size of the aperture in the secondfilter affects the stress of the film deposited on the substrate.Reduced stress is advantageous as it allows thicker films to bedeposited and allows deposition on flexible substrates. The graph showsstress versus filter aperture size (expressed as a % of the ductsectional area) for a 200 mm (8 inch) duct. Without the filter (100%opening) the typical stress for ta-C film is 8 GPa. Use of a filterhaving an 80 mm aperture (16% duct sectional area) reduces the stress toless than 2 Gpa. The stress can be as low as 1 GPa when the filteraperture is 35 mm or 3% duct sectional area in a 200 mm (8 inch) duct.

[0100]FIG. 7 shows the relationship between the quantity ofmacroparticles reaching the substrate versus the filter aperture size,in the range 3-16% duct sectional area (35-80 mm in a 200 mm (8 inch)duct). It can be seen that macroparticle count reduces steadily to aboutzero macroparticles as filter aperture size is reduced from 16-5% ductsectional area. No further reduction in the macroparticle count inachieved by reducing the filter aperture size below 5% duct sectionalarea.

[0101] Referring to FIG. 8, a slight reduction in the deposition rate(A/s) can be seen with decreasing aperture size, over a range of 16-3%duct sectional area, in an 8 inch duct. The rate of reduction ofdeposition is slow, however, compared to the rate of reduction inmacroparticle count over this aperture size-range (compare FIGS. 7 and8). There is also little change in the stress of the film over thisaperture size-range.

[0102] This data shows the advantages in relatively small aperture sizesin accordance with the invention and that, where particle-free coatingis essential, the optimum aperture size will be about 5% duct sectionalarea, for a 200 mm (8 inch) duct. This aperture size combines anacceptable level of deposition with very low macroparticle count and lowstress of the deposited film.

[0103] The invention thus offers the possibility further to reduce thecontamination of films deposited using cathode arc source techniques,even with a conventional duct filter, to provide improved control overthe deposition process and to provide and facilitate ion beam treatmentof the substrate before, during or after the deposition process.

What is claimed is:
 1. A cathode arc source for depositing a coating ona substrate, said source comprising: an anode and a cathode station fora target; and a first filter comprising a filter duct having at leastone bend and first magnetic means for steering plasma through the bendof the filter duct for removal of macroparticles from the plasma,wherein the apparatus further comprises a second filter located betweenthe duct of the first filter and the substrate, for further removal ofmacroparticles from the plasma and comprising a baffle, an aperturethrough which plasma can pass and second magnetic means to provide amagnetic field locally enhanced in the region of the second filter forsteering plasma through the aperture, and wherein the aperture in thesecond filter has an opening of less than 33% of the internal sectionalarea of the filter duct.
 2. The cathode arc source of claim 1, whereinthe aperture in the second filter has an opening of less than 25% of theinternal sectional area of the filter duct.
 3. The cathode arc source ofclaim 1, wherein the aperture in the second filter has an opening ofless than 16% of the internal sectional area of the filter duct.
 4. Thecathode arc source of claim 1, wherein the aperture in the second filterhas an opening of less than 9% of the internal sectional area of thefilter duct.
 5. The cathode arc source of claim 1, wherein the aperturein the second filter has an opening of less than 5% of the internalsectional area of the filter duct.
 6. The cathode arc source of claim 2further comprising a first filter duct attached to a chamber in whichplasma is deposited on the substrate, and wherein the second filter islocated at the exit of the filter duct.
 7. The cathode arc source ofclaim 2 wherein the second filter is a baffle in the form of a filterdisc having a substantially circular aperture.
 8. The cathode arc sourceof claim 7 wherein the disc extends across the width of the filter duct.9. The cathode arc source of claim 7 wherein the disc is less than 2 mmthick.
 10. The cathode arc source of claim 2 further comprising one or aplurality of permanent magnets for providing a local magnetic fieldaround the second filter to steer plasma away from the baffle andthrough the aperture.
 11. The cathode arc source of claim 2 furthercomprising one or a plurality of electromagnets adapted for connectionto a power supply for providing a local magnetic field around the secondfilter to steer plasma away from the baffle and through the aperture.12. The cathode arc source of claim 10 wherein the magnetic fieldprovided around the second filter has a strength in the range of 100 to200 Gauss.
 13. The cathode arc source of claim 2 wherein the secondfilter further comprises a shutter for opening and closing of theaperture.
 14. The cathode arc source of claim 2 further comprising meansin a deposition chamber for generating an ion beam and directing saidbeam at the substrate.
 15. The cathode arc source of claim 2 wherein asource of gas is located at the second filter.
 16. A method of filteringmacroparticles from a beam of plasma emitted from a cathode arc source,the method comprising: using a magnetic field to steer the beam througha first filter comprising a filter duct having at least one bend; andsteering the beam thereafter through a second filter comprising a baffleand an aperture wherein a magnetic field is provided that is locallyenhanced in the region of the second filter so as to steer the beamthrough the aperture, wherein the aperture in the second filter has anopening of less than 33% of the internal sectional area of the filterduct.
 17. The method of claim 16, wherein the aperture in the secondfilter has an opening of less than 25% of the internal sectional area ofthe filter duct.
 18. The method of claim 16, wherein the aperture in thesecond filter has an opening of less than 16% of the internal sectionalarea of the filter duct.
 19. The method of claim 16, wherein theaperture in the second filter has an opening of less than 9% of theinternal sectional area of the filter duct.
 20. The method of claim 16,wherein the aperture in the second filter has an opening of less than 5%of the internal sectional area of the filter duct.
 21. A filter for usein a deposition apparatus having a cathode arc source, a filter duct anda deposition chamber, the filter comprising: a baffle plate having anaperture therethrough; and magnetic field generating means for guidingplasma from the cathode arc source through the aperture, wherein theaperture in the filter has an opening of less than 33% of the internalsectional area of the filter duct.
 22. The filter of claim 21, whereinthe aperture in the filter has an opening of less than 25% of theinternal sectional area of the filter duct.
 23. The filter of claim 21,wherein the aperture in the filter has an opening of less than 16% ofthe internal sectional area of the filter duct.
 24. The filter of claim21, wherein the aperture in the filter has an opening of less than 9% ofthe internal sectional area of the filter duct.
 25. The filter of claim21, wherein the aperture in the filter has an opening of less than 5% ofthe internal sectional area of the filter duct.
 26. The filter of claim22, wherein the baffle plate is substantially circular and the apertureis substantially circular and centrally located.
 27. The filter of claim26, further comprising permanent magnets.
 28. An apparatus forgenerating plasma for deposition upon a substrate, said apparatuscomprising: a main plasma duct, a first cathode arc source, a first sideduct connected to said main plasma duct, a second cathode arc source;and a second side duct connected to said main plasma duct, whereinplasma output from the first cathode arc source is guided by magneticfield into the main plasma duct via the first side duct and plasmaoutput from the second cathode arc source is guided by magnetic fieldinto the main plasma duct via the second side duct, and wherein the mainplasma duct provides a single plasma output from the apparatus.
 29. Theapparatus of claim 28, wherein the first and second side ducts eachcomprise a filter comprising a baffle plate having an aperturetherethrough, and magnetic field generating means for guiding plasmafrom the respective cathode arc source through the aperture, wherein theaperture in the filter has an opening of less than 25% of the internalsectional area of the respective side duct.
 30. The apparatus of claim28, wherein the main plasma duct comprises a filter comprising a baffleplate having an aperture therethrough, and magnetic field generatingmeans for guiding plasma from one of the cathode arc sources through theaperture, wherein the aperture in the filter has an opening of less than25% of the internal sectional area of the main plasma duct.
 31. Theapparatus of claim 28 adapted for simultaneous operation of the firstand second cathode arc sources with different target materials.
 32. Theapparatus of claim 28 further comprising inert gas input and outputports adapted for maintenance of a partial pressure of inert gas in themain plasma duct sufficient to reduce contamination of targets in thecathode arc sources by reactive gas introduced into a deposition chamberattached to the main plasma duct.
 33. A method of depositing a coatingon a substrate, comprising: outputting a first plasma beam from a firstcathode arc source; guiding said first plasma beam through a first sideduct into a main duct; outputting a second plasma beam from a secondcathode arc source; guiding said second plasma beam through a secondside duct into the main duct; in the main duct, combining said first andsecond plasma beams to form a combined beam; and guiding the combinedbeam onto the substrate.
 34. The method of claim 33, wherein said firstand second side ducts each comprise a filter comprising a baffle platehaving an aperture therethrough, and magnetic field generating means forguiding plasma from the respective cathode are source through theaperture, wherein the aperture in the filter has an opening of less than25% of the internal sectional area of the respective side.
 35. Themethod of claim 33, wherein said main duct comprises a filter comprisinga baffle plate having an aperture therethrough, and magnetic fieldgenerating means for guiding plasma from the cathode arc sources throughthe aperture, wherein the aperture in the filter has an opening of lessthan 25% of the internal sectional area of said main duct.